fix #324 to enable more than one HallSensor

Author: Richard Unger

src/sensors/HallSensor.cpp

@@ -53,7 +53,6 @@ void HallSensor::updateState() {
   hall_state = new_hall_state;
 
   int8_t new_electric_sector = ELECTRIC_SECTORS[hall_state];
-  static Direction old_direction;
   if (new_electric_sector - electric_sector > 3) {
     //underflow
     direction = Direction::CCW;

src/sensors/HallSensor.h

@@ -62,6 +62,7 @@ class HallSensor: public Sensor{
 
     // whether last step was CW (+1) or CCW (-1).  
     Direction direction;
+    Direction old_direction;
 
     void attachSectorCallback(void (*onSectorChange)(int a) = nullptr);